Leaf Water Content At Different Positions And Its Relationship With Photosynthesis Of Summer Maize

Accumulation of dry matter in plants depends on canopy photosynthetic rate which is closely related to single leaf photosynthetic capability.The leaf photosynthesis is tightly relevant to its water content.Study on leaf water content?LWC?at different positions and its relationship with photosynthesis under consecutive drought may provide a reference for improving canopy photosynthesis simulation,and identifying and monitoring drought events in summer maize.In this study,the manipulation experiment of the summer maize responses to different watering amounts at three leaf stage was conducted in Gucheng Eco-Environmental and Agro-Meteorological Experiment Station at Baoding city,Hebei Province in 2014.Six different watering treatments?7%,20%,40%,60%,80%and 100%of mean July precipitation during1981-2010,that is to say,the50%,60%,70%,80%,90%,100%of field capacity?were resigned with three replicates per treatment.And the six level watering disposable irrigations were implemented on July 2^nd,2014 when the maize was on 3-leaf stage,after that there were no more irrigation water.Under clear weather condition,the soil water content,the fresh weight and dry weight of the stem,the fresh weight and dry weight of the first?Leaf 1?,third?Leaf 3?and fifth?Leaf 5?leaves on the top of the plant,and net photosynthesis rate?on the same leaf on the same plant?were measured every 1 to 2 weeks.Water stress strongly influenced physiological characteristics of plant.The main conclusions are as follows:?1?The leaf water content of Leaf 1,Leaf 3 and Leaf 5 would drop with the change of the intensity and lasting duration of drought when the summer maize suffered from the water stress.But the falling rates of LWC at different positions are variant.The maximum leaf water contents estimated by hyperbolic relationship at different positions were actually different.The falling rate of leaf water and the estimated maximum leaf water content in Leaf 1 was higher than that in Leaf 3 and Leaf 5.?2?The values of LWC at different positions were appearing difference with the development of consecutive drought.But how the LWC changes with leaf positions was not clear because of the growth stage,soil water content,and leaf senescence and other factors.?3?The leaf water contents of Leaf 1,Leaf 3 and Leaf 5 and their net photosynthetic rates?Pn?showed a quadratic curve relation within a limited range of leaf water content,but the relationship was not true if LWC was under about 72%.When the Pn reduced to zero,the leaf water contents of Leaf 1,Leaf 3,and Leaf 5 were increasing with the leaf position increasing,but the critical leaf water content was reducing as water stress lasting duration increasing.?4?It was worth noting that the fact that the leaf water content of Leaf 1 had a more tight relationship with soil water content and a very strong relationship with photosynthesis.At that time,the lowest leaf water content maintaining net photosynthesis in Leaf 1 was the minimum among the three leaves,which meant Leaf l had better drought tolerance.Leaf 1 could be a typical leaf for identifying drought occurrence and monitoring.?5?Analyzing the process of response of photosynthesis to water changes on Leaf 1,the result showed that the better water content index related tightly with net photosynthesis rates would change from soil water to stem water to leaf water with drought developing,implying the water source change for Leaf 1 could indicate the different drought intensity.